Energy Storage Control System and Method

ABSTRACT

A system for providing power to a power network includes an energy storage device connected to the power network, a sensor connected with the energy storage device for measuring a state of the energy storage device during a rest period, which corresponds to a time span during which a current through the energy storage device is reduced to a level that enables an estimation of a state of the energy storage device. The system further includes a controller connected to the sensor for measuring a state of the energy storage device. The controller selectively establishes rest periods for the energy storage device. The rest periods are established by optimizing between minimization of disruption to normal operation and a need to update a measurement of the state of the energy storage device.

RELATED APPLICATIONS

This application claims the benefits under 35 U.S.C. 119(e) ofProvisional Patent Application Ser. No. 61/751,409, filed Dec. 28, 2012,and of Provisional Patent Application Ser. No. 61/800,208, filed on Mar.15, 2013, both of which are hereby incorporated by reference.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

A vehicle that uses one or more battery systems for supportingpropulsion, start stop, and/or regenerative braking functions can bereferred to as an xEV, where the term “xEV” is defined herein to includeall of the below described electrical vehicles, or any variations orcombinations thereof.

A “start-stop vehicle” is defined as a vehicle that can disable thecombustion engine when the vehicle is stopped and utilize a battery(energy storage) system to continue powering electrical consumersonboard the vehicle, including the entertainment system, navigation,lights, or other electronics, as well as to restart the engine whenpropulsion is desired. A lack of brake regeneration or electricalpropulsion distinguishes a “start-stop vehicle” from other forms ofxEVs.

As will be appreciated by those skilled in the art, hybrid electricvehicles (HEVs) combine an internal combustion engine (ICE) propulsionsystem and a battery-powered electric propulsion system, such as 48volt, 130 volt, or 300 volt systems. The term HEV may include anyvariation of a hybrid electric vehicle, in which features such as brakeregeneration, electrical propulsion, and stop-start are included.

A specific type of xEV is a micro-hybrid vehicle (“mHEV” or“micro-HEV”). Micro-HEV vehicles typically operate at low voltage, whichis defined to be under 60V. Micro-HEV vehicles typically provide startstop, and distinguish themselves from “start-stop vehicles” throughtheir use of brake regeneration. The brake regeneration power cantypically range from 2 kW to 12 kW at peak, although other values canoccur as well. A micro-HEV vehicle can also provide some degree ofelectrical propulsion to the vehicle. If available, the amount ofpropulsion will not typically be sufficient to provide full motive forceto the vehicle.

Full hybrid systems (FHEVs) and Mild hybrid systems (Mild-HEVs) mayprovide motive and other electrical power to the vehicle using one ormore electric motors, using only an ICE, or using both. FHEVs aretypically high-voltage (>60V), and are usually between 200V and 400V.Mild-HEVs typically operate between 60V and 200V. Depending on the sizeof the vehicle, a Mild-HEV can provide between 10-20 kW of brakeregeneration or propulsion, while a FHEV provides 15-100 kW. TheMild-HEV system may also apply some level of power assist, duringacceleration for example, to supplement the ICE, while the FHEV canoften use the electrical motor as the sole source of propulsion forshort periods, and in general uses the electrical motor as a moresignificant source of propulsion than does a Mild-HEV.

In addition, a plug-in electric vehicle (PEV) is any vehicle that can becharged from an external source of electricity, such as wall sockets,and the energy stored in the rechargeable battery packs drives orcontributes to drive the wheels. PEVs are a subcategory of xEV thatinclude all-electric or battery electric vehicles (BEVs), plug-in hybridelectric vehicles (PHEVs), and electric vehicle conversions of hybridelectric vehicles and conventional ICE vehicles. BEVs are drivenentirely by electric power and lack an internal combustion engine. PHEVshave an internal combustion engine and a source of electric motivepower, with the electric motive power capable of providing all or nearlyall of the vehicle's propulsion needs. PHEVs can utilize one or more ofa pure electric mode (“EV mode”), a pure internal combustion mode, and ahybrid mode.

xEVs as described above may provide a number of advantages as comparedto more traditional gas-powered vehicles using only ICEs and traditionalelectrical systems, which are typically 12 volt systems powered by alead acid battery. For example, xEVs may produce fewer undesirableemission products and may exhibit greater fuel efficiency as compared totraditional vehicles and, in some cases, such xEVs may eliminate the useof gasoline entirely, as is the case of certain types of BEVs.

As xEV technology continues to evolve, there is a need to provideimproved power sources (e.g., battery systems or modules) for suchvehicles. For example, it is desirable to increase the distance thatsuch vehicles may travel without the need to recharge the batteries.Additionally, it may also be desirable to improve the performance ofsuch batteries and to reduce the cost associated with the batterysystems.

Conventional xEVs have been found to be functionally limited by theirelectric energy systems that supply power to their electricmotor/generator and vehicle accessories. Typically, an electric motor ispowered by an energy source that needs to store energy suitable forhigh-power discharges as well as for electric demands generated byvarious driving conditions.

Vehicle batteries need be carefully managed to facilitate proper, stableoperation. Various characteristics of the battery may be measured,including the temperature, voltage, current, and others. Other statesmust be estimated from the measurable characteristics, such as the totalcapacity and the “state of charge” (SOC), which is the measure of theamount of energy available in a battery. For xEVs, batterycharacteristics are sensitive to the conditions under which they aremeasured. It can therefore be difficult to both use and characterize thebattery at the same time. In electric or hybrid vehicles, the SOC allowsfor an estimate of the potential distance that may be travelled by thevehicle.

Estimates of SOC are made frequently as part of the typical vehicleoperation. Many means of estimating SOC exist, but most methods use somecombination of two primary methods: voltage lookup and currentintegration. The voltage lookup method utilizes the fact that abattery's open-circuit voltage changes with the state of charge. Thismethod would utilize a transfer function to allow a measured voltage tobe used as a means of determining the SOC. The current integrationmethod starts with a known SOC and total capacity of the battery, andadds/subtracts the electrical charge throughput from the battery.

Each of these methods has significant disadvantages. The voltage lookupmethod suffers from the fact that the battery's terminal voltage is onlyequal to the open-circuit voltage when the current is zero and thebattery is completely equilibrated—something that rarely happens inpractice. Further, for some battery chemistries the open-circuit voltageis nearly constant over a wide range of SOC values, making the voltage apoor predictor of SOC. The current integration suffers from the factthat accuracy degrades gradually due to measurement error and bias andnon-unity battery coulombic efficiencies.

State estimation, and in particular SOC estimation, is important in theutilization of most forms of lithium-ion batteries. This is true becausethe battery can be damaged, or become unstable, if operated outsideproscribed operating conditions. Further, lithium-ion lacks a “redoxshuttle” or “top-charge” reaction that is found for nickel-metal andlead-acid chemistries, in which overcharging the battery (within limits)creates harmless byproducts. Therefore, safe operation requires the SOCbe known with some reasonable level of precision.

Typically, reliable state estimation of an energy storage device, suchas SOC estimation, can only be made infrequently. For example, SOCestimation based on open-circuit voltage can only occasionally beperformed, and only when the vehicle is not being operated. As such, anyestimate of the SOC of the energy storage device increases in inaccuracyduring vehicle operation, as the time since the last accuratemeasurement increases. This effect is especially true of micro-hybrid,mild-hybrid, and hybrid-electric vehicles, due to the relative heavycharge/discharge duty cycles.

To overcome these inaccurate SOC estimations, conventional approachessimply provide a wide margin for operational error. Providing a largemargin for operational error can significantly increase the size of thebattery, increasing the cost of the vehicle overall. Reducing the errormargin without a corresponding increase in accuracy can lead toovercharges and undercharges of the energy storage device, which maycause instability, failure and/or shortening of the life of the energystorage device.

Therefore, there is need for a system and method that enable accurateestimations of a state of an energy storage device used in vehiclebatteries, particularly those (such as micro hybrid, mild hybrid, andhybrid-electric vehicles that utilize high-power brake regeneration andelectric propulsion.

SUMMARY

Disclosed herein is an energy storage control system and method.

In one aspect, a system for providing power to a vehicle power networkincludes an energy storage device connected to the power network, asensor connected with the energy storage device for measuring a state ofthe energy storage device during a rest period, which corresponds to atime span during which a current through the energy storage device isreduced to a level that enables an estimation of a state. The systemfurther includes a controller connected to the sensor for estimating astate of the energy storage device based on available data which mayinclude voltage data, current data, temperature data, and other data.The controller establishes rest periods for the energy storage device.The rest periods are established by optimizing between minimization ofdisruption to normal vehicle operation and a need to update ameasurement of the state of the energy storage device.

In another aspect, a computer-implemented method for controlling theapplication of stored electrical power to a power network is provided.To the power network is connected an ESS to provide stored powerelectrical current to the power network for operation of a power networkload. The ESS includes one or more energy storage devices, which mayinclude lead acid, lithium-ion, NiMH, zinc-bromine, lithium-sulfur, flowbatteries, polyvalent batteries and metal-air batteries and other typesof batteries. Likewise, different types of capacitors may be used, suchas electrolytic, electric double layer capacitors (EDLC), lithiumcapacitor, pseudo-capacitors, asymmetric capacitors, ultra-capacitors,or other types of capacitors. In the case that the ESS includes multipleenergy storage devices, the devices may be connected to each otherelectrically, either directly or via a regulation device, such as aDC/DC convertor, switch, or similar device. One or more of the energystorage devices can also be connected to the vehicle powernet, eitherdirectly or via a regulation device. The method includes establishingenergy storage device rest periods during which a current through theenergy storage device is reduced to a level that enables estimation of astate. Additionally, the rest periods are established by optimizingbetween minimization of disruption to normal vehicle operation and aneed to update a measurement of the energy storage device. The methodfurther includes measuring a state of the “resting” energy storagedevice during the rest periods.

In yet another aspect, a computing system includes a processing unit anda storage device storing instructions that are operable, when executedby the processing unit, to cause the processing unit to perform a methodfor measuring a state of an energy storage device during a rest period.The method includes establishing rest periods during which the currentthrough the energy storage device is reduced to a level that enablesestimation of a state. Reducing the current through the device can beaccomplished by physically disconnecting the device from the vehiclepowernet, or by using a controller to maintain a reduced current. Thismethod also measures the state of the energy storage device, receivesinformation regarding a state of the energy storage device from a sensorduring the rest period, stores the information about the energy storagedevice, and determines a level of confidence in the accuracy of thestored information regarding the state. The method further includesevaluating a level of disruption to normal operation that would becaused by disconnection of the energy storage device, and determining,based upon both the level of confidence in the accuracy of the storedstate and the level of disruption to the strategy that disconnection ofthe energy storage device would cause, when to establish a rest periodfor a new state measurement and storage of a new state of the energystorage device.

In yet another aspect, a system for providing power to a vehicle powernetwork includes an energy storage system having a plurality of energystorage devices that connected to the vehicle power network. The systemfurther includes a controller that establishes rest periods for the eachof the plurality of energy storage devices during which a currentthrough the respective energy storage device is reduced to near zeroamperes, the rest periods established according to a strategy ofoperation so as to not adversely affect the normal operation of thevehicle.

These as well as other aspects, advantages, and alternatives will becomeapparent to those of ordinary skill in the art by reading the followingdetailed description, with reference where appropriate to theaccompanying drawings. Further, it should be understood that thedisclosure provided in this summary section and elsewhere in thisdocument is intended to discuss the embodiments by way of example onlyand not by way of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective view of a vehicle (an xEV) having a batterysystem contributing all or a portion of the power for the vehicle, inaccordance with an embodiment of the present approach;

FIG. 2 is a cutaway schematic view of the xEV embodiment of FIG. 1 inthe form of a hybrid electric vehicle (HEV), in accordance with anembodiment of the present approach;

FIG. 3 is a cutaway schematic view of an embodiment of the xEV of FIG. 1in the form of a micro-hybrid electric vehicle (mHEV), in accordancewith an embodiment of the present approach;

FIG. 4 is a schematic view of the mHEV embodiment of FIG. 3 illustratingpower distribution throughout the mHEV, in accordance with an embodimentof the present approach;

FIG. 5 is a block diagram illustrating components of the controlledenergy storage system;

FIG. 6 is a functional block diagram of elements of the energy storagedevices shown in FIG. 5;

FIG. 7 is an exemplary graph of the charging and discharging of anenergy storage device, such as a battery, in a conventional PRIOR ARTpower system;

FIG. 8 is an exemplary graph of the charging and discharging of anenergy storage device, such as a battery, in the controlled energystorage power system;

FIG. 9 is a flow chart of an embodiment of a battery use strategyperformed a controller;

FIG. 10 is a flow chart of an embodiment of a process involving modelfitting of an energy storage device when the current flow is not nearzero;

FIG. 11 is a flow chart of another embodiment of the battery usestrategy performed by a controller, which optimizes the measurementquality acceptability and capability of setting energy storage device tonear-zero current without undue disruption of normal vehicle operation;

FIG. 12 is a graph illustrating how shorter rest periods lead todecreased accuracy of estimated state of the measurable state.

FIG. 13 is a block diagram illustrating components of an energy storagesystem controller; and

FIG. 14 is a schematic diagram illustrating a conceptual partial view ofan example computer program product.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying figures, which form a part hereof. In the figures, similarsymbols typically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription, figures, and claims are not meant to be limiting. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presentedherein. It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, separated, and designedin a wide variety of different configurations, all of which areexplicitly contemplated herein.

As discussed above, there are several different types of xEVs. Althoughsome vehicle manufacturers, such as Tesla, produce only xEVs and, thus,can design the vehicle from scratch as an xEV, most vehiclemanufacturers produce primarily traditional ICEs. Thus, when one ofthese manufacturers also desires to produce an xEV, it often utilizesone of its traditional vehicle platforms as a starting point. As can beappreciated, when a vehicle has been initially designed to use atraditional electrical system powered by a single lead acid battery andto utilize only an ICE for motive power, converting such a vehicle intoits HEV version can pose many packaging problems. For example, a FHEVuses not only these traditional components, but one or more electricmotors must be added along with other associated components. As anotherexample, a mHEV also uses not only these traditional components, but ahigher voltage battery (e.g., a 48V lithium ion battery module) must beplaced in the vehicle to supplement or replace the 12V lead acid batteryalong with other components such as a belt integrated starter-generator,sometimes referred to as a belt alternator starter (BAS) as described infurther detail below. Hence, if a battery system can be designed toreduce such packaging problems, it would make the conversion of atraditional vehicle platform into an xEV less costly and more efficient.As used herein, the BAS is not intended to be limited to a belt-drivenalternator starter, as other types of drives could be used.

The battery systems described herein may be used to provide power to anumber of different types of xEVs as well as other energy storageapplications (e.g., electrical grid power storage systems). Such batterysystems may include one or more battery modules, each battery modulehaving a number of battery cells (e.g., lithium ion electrochemicalcells) arranged to provide particular voltages and/or currents useful topower, for example, one or more components of an xEV. Presentlydisclosed embodiments include lithium ion battery modules that arecapable of providing more than one voltage. In particular, certaindisclosed battery systems may provide a first voltage (e.g., 12V), forexample, to power ignition of a combustion engine using a traditionalstarter motor and/or support conventional 12V accessory loads, and mayprovide a second voltage (e.g., 48V), for example, to power a BAS and topower one or more vehicle accessories when the combustion engine is notrunning, for use in a micro-hybrid system for example. Indeed, incertain embodiments, not only may a single battery system provide twovoltages (e.g., 12V and 48V), but it can provide them from a packagehaving a form factor equivalent to a traditional lead acid 12V battery,thus making packaging and conversion of a traditional vehicle to a mHEVsimpler, less costly and more efficient.

Present embodiments also include physical battery module features,assembly components, manufacturing and assembling techniques, and soforth, that facilitate providing disclosed battery modules and systemsthat have a desired form factor (e.g., dimensions corresponding to atraditional lead acid battery). Further, as set forth in detail below,the disclosed battery module embodiments include a number of heattransfer devices (e.g., heat sinks, liquid-cooling blocks, heat transferfoams, phase change materials (PCMs), and so forth) that may be used topassively or actively maintain one or more temperatures of the batterymodule during operation.

With the foregoing in mind, FIG. 1 is a perspective view of an xEV 10 inthe form of an automobile (e.g., a car) having a battery system 20 inaccordance with present embodiments for providing all or a portion ofthe power (e.g., electrical power and/or motive power) for the vehicle10, as described above. Although the xEV 10 may be any of the types ofxEVs described above, by specific example, the xEV 10 may be a mHEV,including an ICE equipped with a micro-hybrid system which includes astart-stop system that may utilize the battery system (energy storagesystem) 20 to power at least one or more accessories (e.g., AC, lights,consoles, etc.), as well as the ignition of the ICE, during start-stopcycles.

Further, although the xEV 10 is illustrated as a car in FIG. 1, the typeof vehicle may differ in other embodiments, all of which are intended tofall within the scope of the present disclosure. For example, the xEV 10may be representative of a vehicle including a truck, bus, industrialvehicle, motorcycle, recreational vehicle, boat, or any other type ofvehicle that may benefit from the use of electric power. Additionally,while the battery system 20 is illustrated in FIG. 1 as being positionedin the trunk or rear of the vehicle, according to other embodiments, thelocation of the battery system 20 may differ. For example, the positionof the battery system 20 may be selected based on the available spacewithin a vehicle, the desired weight balance of the vehicle, thelocation of other components used with the battery system 20 (e.g.,battery management systems, vents or cooling devices, etc.), and avariety of other considerations.

FIG. 2 illustrates a cutaway schematic view of an embodiment of the xEV10 of FIG. 1, provided in the form of an HEV having the battery system20, which includes one or more battery modules 22. In particular, thebattery system 20 illustrated in FIG. 2 is disposed toward the rear ofthe vehicle 10 proximate a fuel tank 12. In other embodiments, thebattery system 20 may be provided immediately adjacent the fuel tank 12,provided in a separate compartment in the rear of the vehicle 10 (e.g.,a trunk), or provided in another suitable location in the xEV 10.Further, as illustrated in FIG. 2, an ICE 14 may be provided for timeswhen the xEV 10 utilizes gasoline power to propel the vehicle 10. Thevehicle 10 also includes an electric motor 16, a power split device 17,and a generator 18 as part of the drive system.

The xEV vehicle 10 illustrated in FIG. 2 may be powered or driven by thebattery system 20 alone, by the combustion engine 14 alone, or by boththe battery system 20 and the engine 14. It should be noted that, inother embodiments of the present approach, other types of vehicles andconfigurations for the vehicle drive system may be utilized, and thatthe schematic illustration of FIG. 2 should not be considered to limitthe scope of the subject matter described in the present application.According to various embodiments, the size, shape, and location of thebattery system 20, the type of vehicle, the type of xEV technology, andthe battery chemistry, among other features, may differ from those shownor described.

The battery system 20 may generally include one or more battery modules22, each having a plurality of battery cells (e.g., lithium ionelectrochemical cells), which are discussed in greater detail below. Thebattery system 20 may include features or components for connecting themultiple battery modules 22 to each other and/or to other components ofthe vehicle electrical system. For example, the battery system 20 mayinclude features that are responsible for monitoring and controlling theelectrical and thermal performance of the one or more battery modules22.

FIG. 3 illustrates a cutaway schematic view of another embodiment of thexEV 10 of FIG. 1, provided in the form of a mHEV 10 having the batterysystem 20. As discussed above, the battery system 20 for use with amicro-hybrid system of an mHEV 10 may include a single battery thatprovides a first voltage (e.g. 12V) and a second voltage (e.g. 48V) andthat is substantially equivalent in size to a traditional 12V lead acidbattery used in traditional ICEs. Hence, such a battery system 20 may beplaced in a location in the mHEV 10 that would have housed thetraditional battery prior to conversion to an mHEV. For example, asillustrated in FIG. 3, the mHEV 10 may include the battery system 20Apositioned similarly to a lead-acid battery of a typicalcombustion-engine vehicle (e.g., under the hood of the vehicle 10). Byfurther example, in certain embodiments, the mHEV 10 may include thebattery system 20B positioned near a center of mass of the mHEV 10, suchas below the driver or passenger seat. By still further example, incertain embodiments, the mHEV 10 may include the battery system 20Cpositioned below the rear passenger seat or near the trunk of thevehicle. It should be appreciated that, in certain embodiments,positioning a battery system 20 (e.g., battery system 20B or 20C) in orabout the interior of the vehicle may enable the use of air from theinterior of the vehicle to cool the battery system 20 (e.g., using aheat sink or a forced-air cooling design, as set forth in detail below).

FIG. 4 is a schematic view of an embodiment of the mHEV 10 of FIG. 3having an embodiment of an energy system 21 disposed under the hood ofthe vehicle 10 and includes battery system 20. As previously noted andas discussed in detail below, the battery system 20 may further havedimensions comparable to those of a typical lead-acid battery to limitor eliminate modifications to the mHEV 10 design to accommodate thebattery system 20. Further, the battery system 20 illustrated in FIG. 4is a three-terminal battery that is capable of providing two differentoutput voltages. For example, a first terminal 24 may provide a groundconnection, a second terminal 26 may provide a 12V output, and a thirdterminal 30 may provide a 48V output. As illustrated, the 48V output ofthe battery module 22 may be coupled to a BAS 29, which may be used tostart the ICE 33 during start-stop cycle, and the 12 V output of thebattery module 22 may be coupled to a traditional ignition system (e.g.,starter motor 28) to start the ICE 33 during instances when the BAS 29is not used to do so. It should also be understood that the BAS 29 mayalso capture energy from a regenerative braking system or the like (notshown) to recharge the battery module 22.

It should be appreciated that the 48 V and 12 V outputs of the batterymodule 22 may also be provided to other components of the mHEV 10.Examples of components that may utilize the 48 V output in accordancewith present embodiments include radiator cooling fans, climate controlfans, electric power steering systems, active suspension systems,electric air-conditioning systems, auto park systems, cooled seats,electric oil pumps, electric super/turbochargers, electric water pumps,heated seats, heated windscreen/defrosters, and engine ignitions.Examples of components that may utilize the 12 V output in accordancewith present embodiments include window lift motors, vanity lights, tirepressure monitoring systems, sunroof motor controls, power seats, alarmsystems, infotainment online features, navigation features, lanedeparture warning systems, electric parking brakes, and external lights.The examples set forth above are not exhaustive and there may be overlapbetween the listed examples. Indeed, for example, in some embodiments,features listed above as being associated with a 48 V load may utilizethe 12 V output instead and vice versa.

In the illustrated embodiment, the 48 V output of the battery module 22may be used to power one or more accessories of the mHEV 10. Forexample, as illustrated in FIG. 4, the 48 V output of the battery module22 may be coupled to the heating, ventilation, and air conditioning(HVAC) system 32 (e.g., including compressors, heating coils, fans,pumps, and so forth) of the mHEV 10 to enable the driver to control thetemperature of the interior of the mHEV 10 during operation of thevehicle. This is particularly important in an mHEV 10 during idleperiods when the ICE 33 is stopped and, thus, not providing anyelectrical power via engine charging. As also illustrated in FIG. 4, the48 V output of the battery module 22 may be coupled to the vehicleconsole 34, which may include entertainment systems (e.g., radio, CD/DVDplayers, viewing screens, etc.), warning lights and indicators, controlsfor operating the mHEV 10, and so forth. Hence, it should be appreciatedthat the 48 V output may, in certain situations, provide a moreefficient voltage at which to operate the accessories of the mHEV 10(e.g., compared to 12 V), especially when the ICE 33 is stopped (e.g.,during start-stop cycles). It should also be appreciated that, incertain embodiments, the 48 V output of the battery module 22 may alsobe provided to any other suitable components and/or accessories (e.g.,lights, switches, door locks, window motors, windshield wipers, and soforth) of the mHEV 10.

Also, the mHEV 10 illustrated in FIG. 4 includes a vehicle controlunit/module (VCM) 36 that may control one or more operational parametersof the various components of the vehicle 10, and the VCM 36 may includeat least one memory and at least one processor programmed to performsuch tasks. Like other components of the mHEV 10, the battery module 22may be coupled to the VCM 36 via one or more communication lines 38,such that the VCM 36 may receive input from the battery module 22, andmore specifically, the battery control module (BCM) of the batterymodule 22 (discussed in detail below). For example, the VCM 36 mayreceive input from the battery module 22 regarding various parameters,such as state of charge and temperature, and the VCM 36 may use theseinputs to determine when to charge and/or discharge the battery module22, when to discontinue charging the battery module 22, when to startand stop the ICE 33 of the mHEV 10, whether to use the BAS 29 or thestarter 28, and so forth.

As stated above, in micro-hybrid, mild-hybrid, and hybrid-electricvehicles, various states of an energy storage device that may be one ofa plurality of storage devices of an energy storage system (ESS) need tobe measured or estimated to maintain proper function, includingelectrical propulsion, brake regeneration, and other functions. As anexample of an ESS state, the SOC indicates a current/present capacityexpressed in terms of its rated capacity that a cell has for providingor receiving energy, and is one of the parameters that are required toensure safe charging and discharging of cells of a battery module/pack.As such, SOC provides the current state of cells and enables cells to besafely charged and discharged at a level suitable for cell and batterypack life enhancement. Thus, SOC helps in the management of cells andbattery packs. Furthermore, because SOC is based on deriving the levelof charge from the measured cell voltage and temperature parameters,rechargeable cells may exhibit varying discharge characteristics withtime and temperature.

As known, the SOC is normally measured as a percent of the energystorage device (i.e., cell or battery pack) capacity with a fullycharged energy storage device being 100% and fully discharged being 0%.The definition of fully charged/discharged is dependent on the chemistryand application of the energy storage device. The reference of the SOCcan be expressed relative to the rated capacity of the energy storagedevice, so if an energy storage device has a SOC of 100% it is at fullrated capacity of the energy storage device. The actual capacity of theenergy storage device is known to deteriorate over time, with themaximum capacity and power input/output of the energy storage devicedecreasing over time as the chemistry and internal properties of theenergy storage device deteriorate.

It is known to control power networks in vehicles based on an estimatedcondition of the energy storage device in order to optimize use ofpower, manage the useful life of the energy storage device, and increasefuel economy of the vehicle. With better estimation it may be comepossible for a reduction in cost by downsizing the size of thebatteries. Unfortunately, existing schemes for doing so suffer from aninability to obtain accurate information concerning the status of theenergy storage devices. Highly accurate estimates of a state of anenergy storage device, such as state of charge (SOC), state of health(SOH), capacity, or resistance, can only be made infrequently andindirectly, when the energy storage device is at rest and energy is notbeing drawn from it.

Opportunities to make measurements while the batteries are at rest arerare while the vehicle is in operation. Since the high accuracymeasurements of a state of an energy storage device are madeinfrequently, any stored estimation of a state of an energy storagedevice increases in inaccuracy during the time since the last accuratemeasurement. Since many energy storage devices, like batteries, operatebest under well-controlled conditions, it is important that the state ofan energy storage device is accurately known and that the energy storagedevice is kept operating within an acceptable range of conditions. Oneapproach to address this problem is to “top charge” certain types ofbatteries such that the batteries are fully charged. This approach isinefficient and provides little room for future charging. Anotherapproach has been to accept that measured or estimated states of thebatteries are inaccurate and simply provide a wide margin foroperational error. Unfortunately, this approach is also costly.

Accordingly, the present approach is directed to a power control systemthat performs a battery use strategy that facilitates battery stateestimation during operation of a vehicle. These estimates are performedduring rest periods of the battery, which correspond to a current levelof the battery that enables an evaluation/estimation of the SOC. In oneembodiment, a sensor connected to an energy storage device is used tomeasure a state of the energy storage device during a rest period, whichcorresponds to a time span during which a current through the energystorage device is reduced to a level that enables an estimation of astate, such as resistance, capacity, open circuit voltage (OCV), stateof charge (SOC), and state of health (SOH).

In one embodiment, this estimation enabling current level may be equalto or near zero. This battery use strategy is configured to ensure thatthe battery has regular or selectively established rest periods during adriving mode of the vehicle to facilitate state estimation. The restpoints are established by optimizing against two criteria: 1) minimizingdisruption to the otherwise optimal strategy and 2) urgency of the needto perform state estimation activity. In one embodiment, the rest pointsstrategy is further configured to optimize a duration of the rest eventsversus a frequency of the rest events. Thus, this strategy establishessuitable time periods of rest events that enable a decrease in thescheduling of these rest events. In case of a multiple energy storagesystem, the rest points are selected for one energy storagedevice/component while the remaining energy storage device(s), and/oranother power generation device (such as a generator), can continue tohandle and support any or all vehicle load requirements.

Instances of state estimation can include SOC, remaining capacity,resistance, degradation, and charge imbalance among cells in an energystorage device or energy storage devices in the ESS, among other states.The rest period may also provide opportunity to alleviate any problems,such as imbalance, that may be discovered during the rest period.Alternatively, these problems may be solved during a future rest period.

In accordance with the present disclosure, the SOC is specificallydetermined by comparing a predicted voltage of the battery during therest period to a known relationship between the open-circuit voltage andSOC. As another aspect of the present disclosure, the relationshipbetween open-circuit voltage and SOC may be established at multipletemperatures, and the temperature of the energy storage device may beused in the SOC estimate. Other variables and states may also be used toestimate SOC if these variables and states are known or found to bepredictive of SOC. The ability to predict is true of other states aswell.

Another instance of measurable battery state measurement may be achievedby determining the SOC by setting the OCV to the measured terminalvoltage. The SOC is one of the measurable states, and the relationshipbetween SOC and the OCV is deterministic. If the OCV is known then theSOC can be determined, and vice versa. Because OCV only equals terminalvoltage for a relaxed battery, the OCV needs to be taken on a relaxedbattery over sufficient time for accurate measurement.

Although illustrated as a car in FIGS. 1-4, the type of vehicle 10 maybe implementation-specific, and, accordingly, may differ in otherembodiments, all of which are intended to fall within the scope of thepresent disclosure. For example, vehicle 10 may be a truck, bus,industrial vehicle, motorcycle, recreational vehicle, boat, or any othertype of vehicle. Where the vehicle has an internal combustion engine(ICE), it is located in an engine compartment located within thevehicle.

An exemplary embodiment of an ESS includes one or more energy storagedevices and is configured for the application in a micro hybrid vehicle,which has functions such as start stop, and regeneration braking. Asshown in FIG. 5, an ESS 100 includes a battery module 22 that includescouple of (dual) energy storage devices (E1) 102 and (E2) 104, avoltage/current/power flow regulation device 106 and an ESS controlleror control unit 108. In one embodiment, regulation device 106 may be aDC/DC converter unit. As shown, energy storage device 102 is connectedto electrical accessories 110, and energy storage device 104 isconnected to a starter unit 28 and a generator/alternator unit 29. Asstated above, starter unit 28 and generator/alternator unit 29 can becombined into an integrated starter-generator that provides both starterand generator functions.

As shown, starter unit 28 and generator/alternator are coupled to ICE33, which is in turn coupled to a drivetrain 35. Alternatively,electrical accessories 110 may be positioned between energy storagedevice 102 and regulation device 106. Moreover, electrical accessories110 and energy storage device 102 may be positioned on opposite sides ofregulation device 106. These different positions of energy storagedevice 102 within ESS 100 can support different voltages of energystorage device 102 to meet different power requirements of electricalaccessories 110. In addition, based on power demands ofgenerator/alternator 29, both storage devices 102 and 104 can beconnected to generator/alternator 29, and their respective power flowscan be controlled individually by regulation device 206. In oneembodiment, energy storage device 102 may have characteristics thatrender it suitable for high current operation under high powerconditions, such as during starting and regenerating events.

In one embodiment, energy storage devices 102 and 104 can both belocated on one side of regulation device 106. That is, energy storagedevices 102 and 104 may be located between electrical accessories 110and regulation device 106 or between generator/alternator 29 andregulation device 106. Alternatively, ESS 100, implementable in anyelectrical vehicle, may be a multiple battery system configured tosupport high power loads and provide power redundancy.

Still referring to FIG. 5, vehicle 10 may include one or more vehiclecontrol units, such as VCM 36, which may provide input data to ESS 100that is used to assist in making decisions with respect to estimationsof the measurable states of the one or more energy storage devices. Asdiscussed above, electrical accessories 110 can include a plurality ofaccessories (power consuming loads) that are associated with a powernetwork load, which can vary over time depending upon what differentaccessories and other devices are being powered from time to time. Thepower network load receives electrical power provided by ESS 100 througha power network 250 shown in FIG. 6, such as a vehicle power network.

In one embodiment, E1 100 can be a battery, capacitor, and an energystorage device of any type. Different types of batteries may be used,such as lead acid, lithium-ion, NiMH, zinc-bromine, lithium-sulfur, flowbatteries, polyvalent batteries and metal-air batteries and other typesof batteries. Likewise, different types of capacitors may be used, suchas electrolytic, electric double layer capacitors (EDLC), lithiumcapacitor, pseudo-capacitors, asymmetric capacitors, ultra-capacitors,or other types of capacitors.

In accordance with the present disclosure, E1 102 and E2 204 areselectively controlled by ESS controller 108, in accordance withmeasurable state information obtained through a data network linking ESScontroller 108 to E1 102 and E2 104. ESS controller 108, based oninformation received from VCM 36 and other stored parameters, isconfigured to selectively command regulation device 106 to cause adisconnection of one of energy storage devices E1 102 and E2 104 fromthe power network.

The use of term “disconnect” with reference to energy storage devices E1102 and E2 104 does not necessarily refer to a physical disconnection.Rather, when energy storage devices E1 102 and E2 104 are disconnected,it simply means that they cease supplying more than zero, near-zero orapproximately zero current to or from the power network. In accordancewith the present disclosure, this disconnection is made to reduce thecurrent passing through E1 102 and/or E2 104 to near-zero orapproximately zero. This “disconnection” can be accomplished via areduction in power output setpoint, an actual physical disconnection(e.g., via a switch), or other means.

Approximately or near-zero should be understood to mean exactly zero orsufficiently close to zero to be able to accurately take a measurementof the state of the energy storage device. The exact value of theapproximately or near-zero current will depend heavily on the nature ofthe energy storage device and the particular state of the energy storagedevice measured and may need to be determined empirically. In oneembodiment, approximately or near-zero is preferably from zero to fiveamperes of current, and most preferably, from zero to one hundredmilliamperes of current. In any event approximately or near-zero currentis at whatever low level as is needed to enhance determinations of themeasurable state of energy storage devices E1 102 and E2 104.

Whether a current is sufficiently low depends upon the nature and typeof the battery or other energy storage device and the particularmeasurable state that is desired to be measured. As noted above, in manycases this current may be on the order of approximately one-hundredmilliamperes but may be as high as five amperes or possibly more. Whilethe terms near-zero or approximately zero are intended to includeexactly zero, exactly zero current is not always easily obtained, butnear-zero current is preferably as close to zero as practicable.

As used in this application, the measurable state of one of energystorage devices E1 102 and E2 104 may include the storage deviceconditions of: temperature, voltage, capacitance, polarization, age,resistance, health, remaining life, charge and any other batteryparameters that may be measured. These conditions are provided bycondition sensors 122 and 124 associated with energy storage devices E1102 and E2 104, respectively, which are appropriate to the particularcondition being sensed. Condition sensors 122 and 124 can be connecteddirectly or indirectly to energy storage devices E1 102 and E2 104,respectively.

As stated above, vehicle 10 has ICE 33, and ESS 100 is coupled to apower producing system 140, which includes starter unit 29 andgenerator/alternator 28. During operation, power producing system 140 isconfigured to charge energy storage devices E1 102 and E2 104. In oneembodiment, power producing system 140 includes the means to produceregenerative braking via the alternator, generator, or similar device,as well as optional renewable energy generating devices, e.g., a solarpanel (not shown).

In addition, power producing system 140 includes sensors (not shown)that determine the condition of the power producing units, such astemperature, RPM, power output and the like. The status, or condition,of the power producing units is passed from power producing system 140to ESS controller 108, which is configured to utilize this informationto make determinations when it is best to make a battery statemeasurement of one of or both of energy storage devices E1 102 and E2104.

This determination is preferably done using an optimization proceduredescribed below to minimize disruption of normal operation of vehicle 10when the currents flowing through energy storage devices E1 102 and E2104 are set to near-zero. In addition, operation of the power producingsystem 140 is controlled by VCM 36 based on control signals sent fromESS controller 108.

In addition to energy storage devices E1 102 and E2 104, there may beone or more other energy storage units (not shown), which may be thesame type or a type different from one of energy storage devices E1 102and E2 104.

Referring back to FIG. 5, ESS 100 includes controlled switching units142 and 144 coupled to energy storage devices 102 and 104, respectively,which are selectively actuated by ESS controller 108 to connect theassociated energy storage device 102 or 104 to the power network andthus to any other storage device connected to the power network, to thepower producing system 140 and to vehicle accessories 110. Again, itshould be appreciated that the term “controlled switch unit” is intendedto include any controllable electronic device in which the currentthrough the device may be controlled by provision of control signals toa control input of the device, which may or may not be a conventionalelectronic switch, such as triac or the like. When energy storage device102 or 104 is connected to the network through controlled switch unit142 or 144, charging current may be received through the power networkand the respective controlled switch. Also, when energy storage device102 is connected to the power network, discharging or charging currentmay be drawn from energy storage device 104 connected to the powernetwork through controlled switch unit 144. Each of controlled switchunits 142 and 144 should be understood to be any electrical devicecapable of controlling electrical current flows. When energy storagedevice 102 or 104 is disconnected from the power network by opening ofthe respective controlled switch unit 142 or 144, any charging ordischarging current through energy storage device 102 or 104 isterminated and has a value of zero or near-zero.

In accordance with one important aspect of the present disclosure, it isduring these intentionally created intermittent approximately ornear-zero current periods, that state measurements are made by one ormore of the condition sensors 122 and 124 connected with energy storagedevice 102 and 104, respectively, and communicated to ESS controller108. Condition sensors 122 and 124 may, but do not necessarily include,sensors for determining voltage, temperature, capacitance, current thatmay be directly measured to produce an estimation of the state ofcharge, polarization, resistance or other characteristics.

Now referring to FIG. 7, in the case of known PRIOR ART systems, whilethe battery charging and discharging current 402 does pass through zeroperiods 404 and 406, times of near-zero current are too short, tooinfrequent or both too short and too infrequent to optimize the makingof measurable battery state measurements that can only be optimized bylonger periods of approximately or near-zero current.

The zero points encountered in conventional battery operation as shownin FIG. 7 are merely incidental to the battery or other energy storagedevices rate of transitioning from a charging condition to a dischargingcondition and vice versa. They are not planned or artificially inducedfor the purpose of increasing the estimated accuracy of an internalbattery state. Moreover, the time period of near-zero current is ofteninadequate for taking accurate state measurements. For instance, in thecase of a battery, if the state of charge of is desired to bedetermined, the battery ideally would be allowed to rest for manyminutes before being measured. However, normally such a long period ofrest would be too disruptive to the normal operation of the vehicle. Inaccordance with the present disclosure, a rest period is selected to beless than the ideal but of sufficient duration, so that the relaxationcondition can be projected to estimate what the measured state would be,if there were full relaxation. Depending on the battery in question, atime rest of approximately one minute may be sufficient to estimate thestate of charge. The small duration of the time that the current is zeroor near-zero is merely a characteristic of the storage device isquestion, and the particular times when the zero cross-over points occurmay be too seldom for an optimum rate of periodic monitoring.

On the other hand, as seen in FIG. 8, in accordance with the presentdisclosure, ESS controller 108 is configured to establish preselectedenergy storage device planned rest periods 502. The duration of plannedrest periods 502 may have a certain expectation of completing apreselected desired length of time or time duration during which thecurrent 504 passing through the energy storage device is substantiallyor near zero. However, at any point during the planned rest period 502of preselected desired energy storage device, a vehicle demand couldcause interruption of the intended length of the planned rest period. Anestimate is made of an expected opportunity for an approximate period oftime. However, the actual duration of the planned rest period ends 502when the disruption to the operation of the vehicle caused by theplanned rest period exceeds the need for incremental accuracy inmeasurement. The determination of when or whether the planned restperiods 502 end is continuously evaluated during a rest period. When therest period ends, whatever data was collected before the end of theplanned rest period is used to define a new estimate of the measurablestate of the energy storage device and the confidence of that stateestimate is also determined. The data can be data associated states ofthe energy storage device (i.e., battery data), data associated withstates of operation of the vehicle (i.e., vehicle data external to theenergy storage device), or environmental data. If the confidence of thenew estimate is greater than that of the older estimate, the stateestimate is updated. If not, the older estimate is retained.

Though, these rest periods 54 are planned and not merely incidental tothe battery passing between a discharging condition to a chargingcondition in the course of normal operation. Instead they areartificially imposed. Moreover, rest periods 54 can have an intendedtime duration that is specifically selected to be sufficiently long tofacilitate and enable various state measurements by the conditionsensors 122 and 124, if the time preselected time duration of a plannedrest period actually occurs and is not prematurely ended due to powerdemands by vehicle 10. These relatively lengthy rest periods 54 ofsubstantially near-zero current can be at least tens of seconds long,and from ten seconds to over one minute, depending upon what particularstate measurement is being made and whatever other demands are beingmade on vehicle 10. On the other hand the zero crossing points duringstandard operation of an energy storage device shown in FIG. 6 aretypically of a much shorter duration than needed for accurate estimatesof the state of the energy storage device. The order of charging anddischarging events during driving operation will provide naturalopportunities for defining rest events for the battery. For instance,during coasting, an alternator might be used to support electrical loadswhile the battery is set to near-zero current. Alternatively, inaccordance with one embodiment, for a dual energy storage system, oneenergy storage system might be shut off while the other battery ischarged during regenerative braking.

Typically, during rest periods voltage readings are collected tocorrelate the SOC of the energy storage device. However, the time forthe voltage level of the energy storage device to settle may be longerthan desired. As stated above, some operational modes of vehicle 10 maynot provide the opportunity for such a period of rest to allow the stateof charge to settle. In some instances, it may be acceptable to reduceaccuracy for the benefit of shortening the time requirement for themeasurement. For example, in some instances a full relaxation may notreached even after a period of several minutes, but a shorter period mayenable acquisition of data that allow the determination of modelparameters, which, in turn, allows the prediction of the remainingrelaxation profile with sufficient accuracy.

Now referring to FIG. 9, in one embodiment a flow of operation of ESS100, or program, may begin when vehicle 10 being powered at least inpart by ESS 100 is started at Step 600. During prior operation ofvehicle 100, ESS controller 108 stores the last or most recent measuredstate of each of energy storage devices 102 and 104 and the associatedlevel of confidence of each measurement in a nonvolatile memory unit620. Once vehicle 10 is started again, this last stored statemeasurement and confidence level is retrieved/read by a processing unitof ESS controller 108, at Step 604.

ESS controller 108 is then configured to support normal vehicleoperation, at Step 606, and the time since the last state measurementwas made for each energy storage unit is determined from the states ofassociated clocks (not shown) of ESS controller 108. At Step 608, ESScontroller 108 is configured to determine whether the current of anyparticular energy storage device is near-zero. If the current is alreadynear zero, then one or more ESS states and their confidences may beestimated in Step 618. Assuming the negative from Step 608, then, atStep 610, an estimate of the current quality of, or confidence in, thelast stored measurable battery state determination is made based in parton vehicle run data 631 from associated clocks. In addition, theinherent level of accuracy of condition sensors 122 and 124 for theparticular conditions being sensed may be pre-stored in a sensor infounit 632 of ESS controller 108. In such case, a sensor accuracy level isused in combination with the time of last measurement information tocalculate the present quality or level of confidence in the last statemeasurement. The accuracy information could be gained from sensorspecifications from the manufacturer. Alternatively, ESS controller 108could automatically read sensor accuracy level from data carried by thesensors to insure accuracy.

Next, at Step 612, based on the calculation made at Step 610, adetermination is made as to whether the quality of, or confidence levelin, the last measurable battery state measurement is acceptable. Thisdetermination is made for each of energy storage devices 202 and 204based on a comparison of the previous level of confidence that is storedin the ESS controller 208. This minimum level of confidence isempirically determined for an optimum result.

If the quality level is acceptable, ESS controller 108 is configured torepeat the above cycle, which starts at Step 606. If the quality is notacceptable, at Step 614, ESS controller 108 is configured to determinewhether, based on a number of factors discussed below, a rest period ofnear-zero current for the energy storage unit in question should beestablished. In the negative, ESS controller 108 is configured to cycleback to Step 606. In the affirmative, ESS controller 208 is configuredto determine that which of energy storage devices 102 and 104 may be setto zero, and to actuate the appropriate controlled switch 142 or 144 todisconnect the associated energy storage device 102 or 104 from thepower network 250 to set the current to zero, at Step 616.

During this rest period of near-zero current, one or more measurementsare made and a new estimate of the measurable state(s) of energy storagedevice 102 or 104 is made, at Step 618. At the same time, the newconfidence level(s) in the new estimate(s) are determined. Generally,the confidence level in a new estimate will be highest immediately afterthe new estimate is made.

This new estimate and confidence level is then stored in sensor infounit 632 in lieu of the previous stored amounts, and ESS controller 108proceeds to Step 606 and then Step 608. At Step 608, if the rest periodis still being maintained and the current is near-zero, ESS controller108 is configured to proceed to determine a new state measurement and anew confidence level, at Step 618, and sensor info unit 632 again isupdated, at Step 620. This loop continues repeatedly with repeatedupdates being stored in sensor info unit 632 until the rest period endsand the current is no longer zero. ESS controller 108 is configured tocontinue with recalculating the time since the last update anddetermining the quality or confidence level in the last measurable statedetermination until, once again, a determination is made that thequality is not acceptable, at Step 612.

Calculating the measurable state and confidence level depends oncharacteristics of measurement. Different measurable states (e.g. stateof charge and states of health, etc.) require different standards ofmeasurement. Different types of measurement sensors for determiningdifferent measurable states may require the rest periods to be longerthan others. Some measurable state determinations will produce a lowerlevel of confidence when the rest period is shorter than optimum. On theother hand, some state measurements require more data to estimate thanothers do such that there is a variance in confidence level because ofthe different quantities of data.

For instance, state of charge requires a voltage measurement from arelaxed equilibrated voltage storage device. However, since theequilibration process takes many minutes in some cases, the relaxationprocess must be estimated based upon a number of factors: a projectionof the equilibrated state from a trend of voltage versus time duringrelaxation or a known trend of relaxation versus time for specificcombination of conditions.

The confidence level also depends on the nature of the energy storagedevice and its chemistry. The use pattern of the device that ispredicted based on past experience also affects the expected quality ofthe measurement. With respect to chemistry, if the battery must berelaxed before an accurate measurement can be made, then the nature ofthe battery chemistry and its internal condition will determine how longthe rest period should be for a given level of confidence. For instance,a capacitor might relax quickly allowing a measurement to be madequickly. Alternatively, a large battery with a high capacity might takemany minutes. In addition, the duration of the measurement affects thequantity of data and the duration of the rest period. All the data isdesirably stored regardless of however long the near-zero current restperiod lasts. The duration affects the quality of the estimate becausemeasurable battery state data of measurable state is collected as stateversus time, such as voltage versus time. The trend of change over timeis then fitted and extrapolated to an asymptote at the relaxed state.More data allow a more accurate fit and a better estimate.

Other considerations with respect to establishing a confidence level isthe quality of the measurement. How well the data fits to anelectrochemical relaxation curve is highly dependent on the chemistryand impacts on the quality of the measurement. Noise in the data whichcan be due to sensor phenomenology, for example, can also have aneffect.

With regard to Step 610 of FIG. 9, the quality of the estimated statemeasurement may be determined by considering multiple pieces ofinformation. Increasing the time passed since the last measurementresults in reducing the level of confidence in the estimated measurablestate. The quality of the latest update is dependent on many factorsincluding sensor information concerning the quality of the sensors beingemployed, the chemistry, duration of rest and the fit of the data to themodel. The higher quality current sensors introduce less error and,thus, provide an improved level of confidence in the accuracy of theestimated measurable state.

The quality of the last measurement also depends upon the ability of thesystem to determine the measured state during near-zero or zero current.This ability depends upon the nature of the state being measured. Forexample, if the SOC is to be determined, then accuracy of the estimatedstate measurement depends upon both the accuracy of the voltagemeasurement and the slope of the open circuit voltage (OCV) versus thestate of charge (i.e. OCV vs. SOC) that is characteristic of thespecific battery chemistry.

Determining when to perform a voltage reading depends on two factorswhich are symbolically represented as the decisions made at Steps 612and 614 of FIG. 9. With respect to the question as to whether quality isacceptable, it has already be indicated that more time since the lastupdate leads to reduce quality in the estimate, but measuring acceptablequality also includes other considerations. The sensitivity of thevehicle operation metrics (e.g. fuel mileage economy) againstinaccuracies of the measure state should be considered. The quantitativemetrics of estimate inaccuracy is also a factor. In addition, theexpected benefit of performing a measurement based on the expectedduration until the energy storage device can be set to zero and theduration of the expected rest period of near-zero current should bebalanced against the duration of the event.

The determination, at Step 614 of FIG. 9, as to whether one of energystorage devices 102 and 104 can be set to near-zero current has animpact on vehicle operation. This depends upon present and predictedvehicle operational modes including the expected duration of time untilzero-current is available and the duration of expected zero-currentevents and the like. Specifically, the decision to set the current tozero has an impact on fuel economy and other vehicle metrics, such asvehicle power, potential aging of the battery and other factors.

The two decisions of acceptable quality and whether the energy storagedevice current can be set to near-zero current can be optimized againsteach other by balancing these considerations. This may be done byoptimizing a comparison of the impact on vehicle function by performingmeasurements instead of maintaining normal operation and the negativeimpact that poor quality estimates may have the energy storage devicessuccessful continued operation.

This is preferably done by using an optimization process (method) likethat shown in FIG. 10 to determine in real time whether to perform anoptimization event. The optimization of one or more potential costfunctions should be based on several considerations. Energy storagedevice lifetime, fuel economy, vehicle stability and passenger comfortshould be considered. Also, the impact upon other components givenoptimization of a subset should be factor. For example, optimization ofone energy storage device may increase the load requirements on otherbatteries or an alternator or the like.

Now referring to FIG. 10, in accordance with the proposed battery usestrategy ESS controller 108 is configured to trigger/initiate a restperiod (i.e., event of near zero current) of at least one of energystorage devices 102 and 104, at Step 702. ESS controller 108 thendetermines whether the current is still near or equal to zero, at Step704. In the affirmative, ESS controller 108 keeps on accumulating datato determine the desired state of energy storage device 102 or 104, atStep 706. Otherwise, ESS controller 108 is configured to use thecollected data while the current was near or equal to zero and any otherdata collected when the current was different from zero, to fit it in abattery model, at Step 708. The battery model can be one of anelectrochemical model, an equivalent circuit model, or any othersuitable model. Following the model fitting of the collected data, ESScontroller 108 determines a measurement uncertainty using at least oneof uncertainty models, which relate to measurement uncertainty,uncertainty in the model fitting, or any other source of uncertainty, atStep 710. Subsequently, ESS controller 108 uses the measured data andevaluated uncertainty to estimate a battery state value or level and alevel of the state uncertainty, at Step 712.

Now referring to FIG. 11, the time since the last state measurement, ortime since the last updated, is provided as vehicle run data 631 fromthe states of associated clocks 630 of ESS controller 108 for each ofthe energy storage devices 102 and 104. From this run data 631, at Step802, a determination is made by the ESS controller 208 of the expectedduration of a rest period, if one has been initiated. Also, the presentquality of the measurable state estimate is made by ESS controller 108,at Step 804, that also received vehicle run data 631. The calculation,made at Step 804, of present state estimate quality is also based onsensor info unit 632, including sensor accuracy. The determination, atSteps 802 and 804, are used to determine the expected improvement in theestimate if a new measurement is made, at Step 806. This estimate isthen passed to an advantage branch of the process, at Step 808.

Following Step 808, ESS controller 108 is configured to produce a costmetric for a measurement, at Step 803. At Step 805, ESS controller 108then uses the cost factor to determine a reduced cost due to obtainingan improved estimate of the measured state, which then added to arunning total, at Step 807. The cost factor is determined based onvehicle cost metrics 809 including fuel economy, an aging impact factor,and other potential factors.

On the other side of the determination to establish a planned restperiod, at Step 810, ESS controller 108 quantifies (evaluates) a levelof disruption to vehicle 10 that will occur due to a planned rest periodbeing established. ESS controller 108 passes this quantification to adisadvantage branch of the process, at Step 812. During the disadvantagebranch, ESS controller 108 determines each cost metric, at Step 811.Then at Step 813, ESS controller 108 uses the vehicle costs metrics fromthe vehicle cost metrics 809, and at Step 813, the increased cost due tovehicle impact is determined and this cost is added to a running total.The running total of the respective cost of causing a rest period areused, at Step 814, to determine whether the reduced advantage costsoutweigh the increased vehicle cost. If the answer is affirmative, atStep 816, a planned rest period is initiated if one is not occurring, oris continued, if a planned rest period has already been started. If thedecision is negative, at Step 818, the rest period is stopped if alreadybegun and is not started if one has not already begun.

Referring now to FIG. 12, a graph is provided that illustrates thelessening of estimated measurable state as time passes after a statemeasurement during a rest period. An uncertainty in projection 114 isdue to uncertainty of measurements (precision and accuracy), limitedamounts of data and appropriateness of any model that may be used to fitthe data.

In general, the stored use strategy of the present disclosure ensuresthat there will be occasional or regular rest periods established tofacilitate state measurement activity during driving of vehicle 10. Thetiming of the rest periods will be chosen against the general criteriaof minimizing disruption to the otherwise optimal or normal vehicleoperation versus the urgency of a need to perform a measurable statedetermination as well as duration of rest periods versus the frequencyof rest periods. In a hybrid vehicle, the rest periods may occur whenICE 33 can accept the load, via the alternator or generator. The restperiod opportunity depends on the type of vehicle. For a dual-batterysystem, one battery can rest while the other accepts the load. Inaddition, measurable battery state measurement will includeconsideration of problems discovered as a result of state estimation,such as the need to perform battery cell balancing.

As shown in FIG. 13, ESS controller 108 includes a normal operationprogram/module 1002, a rest period determination module 1004, a stateestimation module 1006, and a battery model fitting module 1008. ESScontroller 208 further includes a micro-processing unit 1010, and amemory unit 1012. Micro-processing unit 1010 can be implemented on asingle-chip. For example, various architectures can be used includingdedicated or embedded microprocessor (μP), a microcontroller (μC), orany combination thereof. Memory unit 1012 may be of any type of memorynow known or later developed including but not limited to volatilememory (such as RAM), non-volatile memory (such as ROM, flash memory,etc.) or any combination thereof, which may store software that can beaccessed and executed by the processing units, for example.

In some embodiments, the disclosed method may be implemented as computerprogram instructions encoded on a computer-readable storage media in amachine-readable format. FIG. 14 is a schematic illustrating aconceptual partial view of an example computer program product 1100 thatincludes a computer program for executing a computer process on acomputing device, arranged according to at least some embodimentspresented herein. In one embodiment, the example computer programproduct 1100 is provided using a signal bearing medium 1101. The signalbearing medium 1101 may include one or more programming instructions1102 that, when executed by a processing unit may provide functionalityor portions of the functionality described above with respect to FIGS.1-12. Thus, for example, referring to the embodiment shown in FIGS.9-11, one or more features of their respective steps, may be undertakenby one or more instructions associated with the signal bearing medium1101.

In some examples, signal bearing medium 1101 may encompass anon-transitory computer-readable medium 1103, such as, but not limitedto, a hard disk drive, memory, etc. In some implementations, the signalbearing medium 1101 may encompass a computer recordable medium 1104,such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs,etc. In some implementations, signal bearing medium 1101 may encompass acommunications medium 1105, such as, but not limited to, a digitaland/or an analog communication medium (e.g., a fiber optic cable, awaveguide, a wired communications link, etc.).

One or more of the disclosed embodiments, alone or in combination, mayprovide one or more technical effects useful in the controlling ofenergy storage systems in micro and mild hybrid vehicles. The technicaleffects and technical problems in the specification are exemplary andare not limiting. It should be noted that the embodiments described inthe specification may have other technical effects and can solve othertechnical problems.

While only certain features and embodiments of the disclosure have beenillustrated and described, many modifications and changes may occur tothose skilled in the art (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters (e.g., temperatures, pressures, etc.), mounting arrangements,use of materials, colors, orientations, etc.) without materiallydeparting from the novel teachings and advantages of the subject matterrecited in the claims. The order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. It is, therefore, to be understood that the appended claimsare intended to cover all such modifications and changes as fall withinthe true spirit of the disclosure. Furthermore, in an effort to providea concise description of the exemplary embodiments, all features of anactual implementation may not have been described (i.e., those unrelatedto the presently contemplated best mode of carrying out the invention,or those unrelated to enabling the claimed invention). It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerous implementationspecific decisions may be made. Such a development effort might becomplex and time consuming, but would nevertheless be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure, without undueexperimentation.

1. A system for providing power to a vehicle power network, comprising:an energy storage device connected to the power network; a sensorconnected to the energy storage device for measuring a state of theenergy storage device during a rest period, wherein the rest periodcorresponds to a time span during which a current through the energystorage device is reduced to a level that enables an estimation of astate of the energy storage device; and a controller that receives datafrom the sensor and estimates the state of the energy storage devicebased on data, wherein the controller establishes the rest period byoptimizing between minimization of disruption to normal vehicleoperation and a need to update a measurement of the state of the energystorage device.
 2. The system of claim 1, wherein the data is batterydata.
 3. The system of claim 1, wherein the data is vehicle dataexternal to the battery.
 4. The system of claim 1, wherein the currentlevel that enables the state estimation is approximately zero.
 5. Thesystem of claim 1, further comprising: an additional sensor forproviding information about a condition of a power producing unit to thecontroller, wherein the controller utilizes the information from thepower producing unit to establish additional rest periods when the powerproduction unit can handle an increased load resulting from adisconnection of the energy storage device from the power network. 6.The system of claim 1, further comprising: an additional energy storagedevice connected to the power network for providing additional currentto the power network for operation of a power network load; and anadditional sensor that receives data from the sensor and measures astate of the additional energy storage device when the additional energystorage device has been disconnected from the power network by thecontroller to reduce stored electrical current to near-zero during restperiods for the additional energy storage device, the controllerestablishing additional rest periods for the energy storage device whenthe additional energy storage device is capable of handling loadrequirements of the power network.
 7. The system of claim 1, wherein thecontroller determines a length of time since a last state measurement ofthe energy storage device, and calculates a level of confidence in theaccuracy of the last state measurement of the energy storage devicebased at least in part on the length of time since the last measurementof the state of the energy storage device.
 8. The system of claim 1,wherein the sensor has a predetermined level of accuracy, and whereinthe controller stores the predetermined level of accuracy of the sensor,and calculates a level of confidence in the accuracy of a last statemeasurement of the energy storage device based at least in part by thepredetermined level of accuracy of the sensor.
 9. The system of claim 1,wherein the controller is programmed to: store a preselected minimumlevel of confidence in an energy storage device state measurement,calculate a level of confidence in a measurement obtained from a laststate measurement of the energy storage device, compare the measurementof the last energy storage device state measurement with the preselectedminimum level of confidence, and disconnect the energy storage device toenable the updated state measurement of the energy storage device basedat least in part on the comparison.
 10. The system of claim 1, whereinthe controller is programmed to: determine whether setting the energystorage device current to the level that enables an estimation of thestate will have a negative impact on the normal operation, compare themeasurement of a last state measurement of the energy storage devicewith a preselected minimum level of confidence, and disconnect theenergy storage device to enable a new state measurement of the energystorage device based on both the determination and the comparison. 11.The system of claim 1, wherein the power network is a vehicle powernetwork.
 12. A computer-implemented method for controlling theapplication of stored electrical power to a vehicle power network,wherein an energy storage device is connected to the vehicle powernetwork to provide stored power electrical current to the power networkfor operation of a power network load, the method comprising:establishing energy storage device rest periods during which a currentthrough the energy storage device is reduced to a level that enables anestimation of a state of the energy storage device, wherein the restperiods are established by optimizing between minimization of disruptionto normal vehicle operation and a need to update a measurement of thestate of the energy storage device; and measuring a state of the energystorage device during the rest periods.
 13. The computer-implementedmethod of claim 12, further comprising: controlling a power producingunit connected to the power network for providing produced power to theenergy storage device when connected to the power network.
 14. Thecomputer-implemented method of claim 12, further comprising: selectivelyproviding additional current to the power network from an additionalenergy storage device for operation of the power network load.
 15. Thecomputer-implemented method of claim 12, wherein the energy storagedevice is a first energy storage device, and the method furthercomprises: providing power to the power network from a second energystorage device, and establishing the rest periods for the first energystorage device when the second energy storage device is capable ofhandling load requirements of the power network.
 16. Thecomputer-implemented method of claim 12, further comprising:establishing the rest periods when a power producing unit can handle anincreased load resulting from disconnection of the energy storagedevice.
 17. The computer-implemented method of claim 12, furthercomprising: storing a most recent measurement by a sensor of the stateof the energy storage device; and storing a level of confidence ofstored results of the state measurement of the energy storage device.18. The computer-implemented method of claim 12, further comprising:determining a length of time since a last state measurement; andcalculating a level of confidence in the accuracy of the last statemeasurement based at least in part on a length of time since the laststate was measured.
 19. The computer implemented method of claim 12,further comprising: storing a predetermined level of accuracy of thesensor; and calculating a level of confidence in the accuracy of a laststate measurement based at least in part by the predetermined level ofaccuracy of the sensor.
 20. The computer-implemented method of claim 12,further comprising: storing a preselected minimum level of confidence ina state measurement; calculating a level of confidence in a measurementobtained from a last state measurement; comparing the measurement of thelast occurrence of a state measurement with the preselected minimumlevel of confidence; and disconnecting the energy storage device toenable a new state measurement based at least in part on saidcomparison.
 21. The computer-implemented method of claim 12, furthercomprising: determining whether setting the energy storage devicecurrent to the level that will enables estimation of the state of theenergy storage system will have a negative impact on normal operation;comparing the measurement of a last occurrence of a state measurementwith a preselected minimum level of confidence; and disconnecting theenergy storage device to enable a new state measurement based inresponse to both the determining means and the comparing means.
 22. Acomputing system, comprising: a processing unit and a storage devicestoring instructions that are operable, when executed by the processingunit, to cause the processing unit to perform a method for measuring astate of an energy storage device during a rest period, wherein theenergy storage device provides power over a vehicle power network, themethod comprising: establishing rest periods during which a currentthrough the energy storage device is reduced to a level that permits anestimation of a state of the energy storage device, wherein reducing thecurrent can be accomplished by physically disconnecting the energystorage device from the vehicle power network, or by using a controllerto maintain the reduced current is disconnected from the power networkfor operation of a power network load to reduce current through theenergy storage device to near zero to measure the state of the energystorage device; receiving information regarding a state of the energystorage device from a sensor during the rest period, and storing theinformation about the energy storage device; determining a level ofconfidence in the accuracy of the stored information regarding thestate; evaluating a level of disruption to normal operation that wouldbe caused by disconnection of the energy storage device; anddetermining, based upon both the level of confidence in the accuracy ofthe stored state and the level of disruption to the strategy thatdisconnection of the energy storage device would cause, when toestablish a rest period for a new state measurement and storage of a newstate of the energy storage device.
 23. The computing system of claim22, further comprising: controlling an electrical power producing unitconnected to the power network for providing produced power to chargethe energy storage device when connected to the power network; anddetermining when to establish the rest period based in part on an amountof electrical power being produced by the power producing unit to chargethe energy storage device.
 24. The computing system of claim 22, whereinthe energy storage device is a first energy storage device andselectively providing additional current to the power network from asecond storage device for operation of the power network load.
 25. Thecomputing system of claim 22, wherein the energy storage device is afirst energy storage device and wherein the method further comprises:controlling a second storage device connected to the power network; andestablishing the rest periods for the first energy storage device onlywhen the second energy storage device is capable of handling loadrequirements of the power network.
 26. The computing system of claim 22,further comprising: monitoring operation of a power producing unit; andestablishing the rest periods when the power producing unit can handlean increased load resulting from disconnection of the energy storagedevice.
 27. The computing system of claim 22, further comprising:determining a length of time since a last measurement of the state ofthe energy storage device connected to a regenerative power source; andcalculating the level of confidence in the accuracy of the last statemeasurement based at least in part on the length of time since the laststate measurement.
 28. A computer-implemented method for controllingprovision of power to a power network, comprising: providing electricalcurrent to the power network from an energy storage device for operationof a power network load; reducing the current through the energy storagedevice with a switch to a level that enables an estimation of a state ofthe energy storage device for a rest period; and measuring a state ofthe energy storage device within a certain level of accuracy during therest period.
 29. The computer-implemented method of claim 28, furthercomprising: establishing a strategy of operation; monitoring operationof a power producing unit; storing a last measurement of a state;establishing a declining level of confidence in the last measurement ofthe state; and establishing when the rest periods occur by optimizingbetween minimization of disruption to the normal operation and thedeclining level of confidence in the last measurement of the state. 30.A system for providing power to a vehicle power network, comprising: afirst energy storage device connected to the vehicle power network; asecond energy storage device connected to the vehicle power network; acontroller that establishes rest periods for the each of the firstenergy storage device and the second energy storage device during whichcurrent through the respective energy storage device is reduced to alevel that enables an estimation of the state of the energy storagedevice, the rest periods established according to a strategy so as tonot adversely affect the normal operation of the vehicle.